1. Field of the Invention
The present invention relates to a tool transfer mechanism for machine tools in which a plurality of tools are stored in a storage magazine and are selectively transferred from the storage magazine to a tool spindle on a machine or vice versa.
2. Discussion of the Background
In general, in a vertical machine tool with an automatic tool changing apparatus, a spindle is vertically journalled to a spindle head. A plurality of tools are stored in a storage magazine with respective axes thereof being horizontally oriented. Therefore, in exchanging tools between the spindle and the storage magazine, a tool transfer mechanism has to change the posture of the tool from one where an axis of the tool is vertical to another where it is horizontal, or vice versa, during transfer of the tool.
One example of such a tool transfer mechanism is disclosed in Japanese Patent Application Publication No. 22636/1983, wherein a tool holder which detachably carries a tool is shifted by the tool transfer mechanism between a gateway position of a tool storage magazine and a tool exchange position adjacent a spindle. The tool transfer mechanism has a fork which is attached to a middle portion of a cam shaft and is separably engageable with the tool holder. The cam shaft is rotatably connected to a piston rod of a hydraulic cylinder.
A twisted grooved cam is axially formed on a periphery of the cam shaft and is engaged with a roller that is attached to a fixed frame, so that the cam shaft is rotated by a 90.degree. angle in accordance with its axial movement. A swing plate which is rotatably mounted on the fixed frame is engaged with a spline portion of the cam shaft. A pair of guide bars are fixed to the swing plate to guide the tool holder while the same is being shifted by the fork.
As a result, when the cam shaft is moved by the hydraulic cylinder to shift the tool holder between the gateway position and the exchange position, it is rotated by a 90.degree. angle because of engagement of the grooved cam with the roller. The fork, the swing plate and the guide bars are simultaneously rotated so that a tool carried in the tool holder changes its posture between a horizontal one at the gateway position and a vertical one at the exchange position. However, in such tool transfer mechanism, insofar as the long guide bars are necessary to guide the tool holder, the tool transfer mechanism as a whole becomes cooperatively large and complex.